[mthod for fabricating piezoelectric workpiece with augmenting surface electrode]

ABSTRACT

A method for fabricating piezoelectric workpieces with augmenting surface electrodes is disclosed for improving fabrication and operation reliability of the workpieces. The fabrication method forms a plurality of function electrodes on the surface of the body of the workpiece and the function electrodes being connected in the electric circuit of the piezoelectric system. At least one of the function electrodes has a shape with a contour of at least one acute angle. At least one polarization augmenting electrode is then formed on the surface of the body proximate to the acute angle, the polarization augmenting electrode and the proximate function electrode thereof constituting a gross electrode when connected electrically together. Electric dipoles of grain molecules of the body are then polarized utilizing the gross electrode, the gross electrode substantially cancels the acute angle when paired with one of the function electrodes and connected to a polarization voltage for implementing the polarization. The polarization voltage polarizes electric dipoles of grain molecules of the body in between the pair so that the boundary region between different polarization orientation distribution regions within the piezoelectric workpiece is smoothed without any acute angle.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a divisional of a prior application Ser. No.10/064,465, filed Jul. 17, 2002, which claims the priority benefit ofTaiwan application serial no. 91114481, filed Jul. 01, 2002.

BACKGROUND OF INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates in general to piezoelectricity and, inparticular, to the protection and reliability improvement ofpiezoelectric workpieces utilizing augmenting surface electrodes. Moreparticularly, this invention relates to a method for fabrication ofpiezoelectric workpiece with augmenting surface electrode.

[0004] 2. Technical Background

[0005] Piezoelectricity is useful in various applications. With theadvancements in material science and microelectronic technology,piezoelectric apparatuses are found in ever more equipment, scientific,industrial, or commercial. Typical examples include piezoelectrictransformer in the power system of portable devices such as notebookcomputers, personal digital assistant (PDA), and cellular phones,accelerometer and gyroscope for commercial navigation devices andpiezoelectric signal filter in industrial sensory and control systems,among others.

[0006] Workpieces of different physical shapes and sizes of thepiezoelectric nature are the center core of piezoelectric systems.Piezoelectric workpieces are made of materials capable of beingfabricated to exhibit piezoelectricity. Typically, selected powderedmaterial such as lead zirconate titanate (PZT) is made into thepiezoelectric workpiece piece of the desired shape and size in asintering-based fabrication procedure. During the high-temperaturesintering phase, grains in a molded workpiece are grown. For somecommercial piezoelectric material, sintering brings up usefulpiezoelectricity, but for many others, further processing is necessary.For these materials, a bulk workpiece does not possess piezoelectricityuntil it is processed in a polarization procedure.

[0007] Thermal polarization procedures generally known as poling areemployed to orient the electric dipoles in the grain molecules of theworkpiece. The aim is so that the grain molecules, in the bulk, exhibita gross polarization that in general conforms to the desired orientationfield pattern of the piezoelectric device for certain designed operatingcharacteristics. To implement the polarization processing on theworkpiece under fabrication, electric fields of relatively high voltageare necessary. High voltage needs to be supplied across electrodesadhered (fixedly attached) to the surface of the workpiece for aprolonged period of time so as to facilitate the poling.

[0008] One obvious problem with the conventional technique ofpiezoelectric workpiece fabrication is related to the above-mentionedhigh-voltage poling. In general, the electrodes used for polarizationprocessing are also the functional electrodes of the same workpiece forits future normal operation. Considering that the polarization voltageis, typically, several to tens of times that of the voltage that will bepresent across the function electrodes of the workpiece during normaloperation, it is likely that the polarization processing duringfabrication, if not designed properly, becomes damaging to the workpieceitself. Two possible causes are responsible for such destructivepolarization processing results accompanying the relatively-highpolarization voltage.

[0009] The first is understood to be related to the uneven internal bodystress arising from the poling of molecular electric dipoles in theworkpiece. As the poling is implemented for an extended period of time,material crystalline grains within the workpiece located between theelectrodes supplied with a high electric potential difference aregradually polarized. As the electric dipoles of those grains aregradually polarized, the grains also exhibit an ever more significantpiezoelectricity.

[0010] Gradually, the workpiece thus experiences partial piezoelectricdeformation in the body portion generally between the poling electrodes.Since, as mentioned, this poling voltage is times higher than that ofnormal operation, such partial structural deformation is likely tocreate significant internal mechanical stress in the boundary regionwhere the polarized and un-polarized regions meet. Such body stress issometimes sufficient to break the workpiece into pieces. This isparticularly the case if one or more of the electrodes for apiezoelectric workpiece are patterned into shapes with acute angles.Such electrode shape patterns are more likely to induce high regionalconcentrations of internal mechanical stress within the piezoelectricworkpiece.

[0011] The second cause is in relation to the phenomenon of pointdischarge across the electrodes used for polarization processing. This,also, is particularly true if an electrode for a piezoelectric workpieceis patterned into a shape with acute angles to induce point dischargeduring polarization processing. A point discharge during the polingprocessing of workpiece fabrication is likely to be catastrophic sincethe body of the workpiece may be fatally broken apart into pieces. Surgecurrent in association with a point discharge across electrodes of apiezoelectric workpiece inevitably gives rise to abrupt increase inlocal body mechanical stress along the path of the discharge current.Frequently, as had been observed, such an abrupt regional stressincrease breaks up the workpiece into pieces.

[0012] After fabrication, operation of a piezoelectric workpiece, as iswell known, involves the mechanical/electrical energy conversion.Sustained and reliable operation of a workpiece in a piezoelectricsystem is dependent on several factors. Among these factors, the bulkphysical structural characteristics in the workpiece is an importantone.

[0013] Although the electric voltages in relation to the operation of apiezoelectric workpiece are relatively much lower than those employedduring the fabrication phase for the same workpiece, however, aworkpiece is only exposed to fabrication electric fields for the matterof a few hours. By contrast, reliable operation of a piezoelectricsystem requires that the workpiece be used for thousands of hours. Thus,stress concentration build-ups within the body of a piezoelectricworkpiece not sufficient to fail the device during the fabrication phasemay still fail the device during prolonged periods of normal operation.For example, if the piezoelectric device is operated in non-optimizedmodes, the internal heat build-up is a likely factor to amplify themechanical stress concentration to a level sufficient to fail thedevice.

[0014] For the foregoing reasons, there is a need for a method to avoidthe formation of regions with abrupt polarization orientation alterationinside the body of a piezoelectric workpiece that may lead to mechanicalstress concentrations and eventually result in structural failure,either during the manufacturing phase or during normal operation.

[0015] There is also a need for a method to smooth the polarizationorientation alterations inside the body of a piezoelectric workpiecethat prevents the build-up of mechanical stress concentrations todamaging levels, either during the manufacturing phase or during normaloperation.

SUMMARY OF INVENTION

[0016] The invention is directed to augmenting surface electrodes forpiezoelectric workpieces for improving fabrication and operationreliability thereof. A method for fabricating piezoelectric workpieceswith augmenting surface electrodes is disclosed for improvingfabrication and operation reliability of the workpieces. The fabricationmethod forms a plurality of function electrodes on the surface of thebody of the workpiece and the function electrodes being connected in theelectric circuit of the piezoelectric system. At least one of thefunction electrodes has a shape with a contour of at least one acuteangle. At least one polarization augmenting electrode is then formed onthe surface of the body proximate to the acute angle, the polarizationaugmenting electrode and the proximate function electrode thereofconstituting a gross electrode when connected electrically together.Electric dipoles of grain molecules of the body are then polarizedutilizing the gross electrode, the gross electrode substantially cancelsthe acute angle when paired with one of the function electrodes andconnected to a polarization voltage for implementing the polarization.The polarization voltage polarizes electric dipoles of grain moleculesof the body in between the pair so that the boundary region betweendifferent polarization orientation distribution regions within thepiezoelectric workpiece is smoothed without any acute angle.

BRIEF DESCRIPTION OF DRAWINGS

[0017] These and other features, aspects, and advantages of theinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings where.

[0018]FIG. 1 schematically illustrates the abrupt alteration of theelectric dipole polarization field inside the structural body of apiezoelectric workpiece in the region proximate to an acute-angled areaof a function electrode.

[0019]FIG. 2 schematically illustrates the smoothing of the polarizationfield inside the structural body of a piezoelectric workpiece of FIG. 1in the region proximate to the acute-angled area of the functionelectrode in accordance with an embodiment of the present invention.

[0020]FIG. 3 is a top view illustrating the placement of an augmentingsurface layer for a generally elliptically-shaped function electrode inaccordance with an embodiment of the present invention.

[0021]FIG. 4 is a top view illustrating the placement of anotheraugmenting surface layer for the generally elliptically-shaped functionelectrode of FIG. 3 in accordance with an embodiment of the presentinvention.

[0022]FIG. 5 is a top view illustrating the location of afabrication-phase augmenting surface electrode on the surface of apiezoelectric workpiece having a generally elliptically-shaped functionelectrode in accordance with an embodiment of the present invention.

[0023]FIG. 6 is a top view illustrating the location of anotherfabrication-phase augmenting surface electrode on the surface of thepiezoelectric workpiece having a generally elliptically-shaped functionelectrode of FIG. 5 in accordance with an embodiment of the presentinvention.

[0024]FIG. 7 is a top view illustrating the electrode pattern of thepiezoelectric workpiece of FIGS. 5 and 6 after the completion of thefabrication phase thereof.

[0025]FIG. 8 schematically illustrates the cross-section of apiezoelectric workpiece without the augmenting surface layer.

[0026]FIG. 9 schematically illustrates the piezoelectric workpiece ofFIG. 8 having incorporated an augmenting surface layer in accordancewith an embodiment of the present invention.

[0027]FIG. 10 is a cross-sectional view illustrating the contact ofpoling electrodes with both the function and the augmenting surfaceelectrodes in accordance with an embodiment of the present invention.

[0028]FIG. 11 is a cross-sectional view illustrating the contact of apoling electrode that is used directly as an augmenting surface layer inaccordance with an embodiment of the present invention.

[0029]FIG. 12 illustrates the point discharge induced at theacute-angled area of a function electrode of a piezoelectric workpiece.

[0030]FIG. 13 illustrates the avoidance of point discharge at theacute-angled area of the function electrode of FIG. 12 in accordancewith an embodiment of the present invention.

[0031]FIG. 14 illustrates the piezoelectric workpiece of FIG. 9 havingan additional function electrode.

[0032]FIG. 15 illustrates the piezoelectric workpiece of FIG. 14 havingincorporated another augmenting surface layer in accordance with anembodiment of the present invention.

[0033]FIG. 16 illustrates the relative placement of an augmentingsurface layer with respect to an arbitrary-shaped function electrode ofa piezoelectric workpiece in accordance with an embodiment of thepresent invention.

[0034]FIG. 17 illustrates the relative placement of another augmentingsurface layer with respect to the function electrode of thepiezoelectric workpiece of FIG. 16 in accordance with an embodiment ofthe present invention.

DETAILED DESCRIPTION

[0035] The best modes of implementation of the fabrication of thepiezoelectric workpiece of the present invention will be described inthe following paragraphs.

[0036] In a perspective view, FIG. 1 schematically illustrates theabrupt alteration of the electric dipole polarization field inside thestructural body of a piezoelectric workpiece in the region proximate toan acute-angled area of a function electrode. As is illustrated, asection 102 of a piezoelectric workpiece 100 is shown to have a functionelectrode 110 adhered to the top surface thereof. An opposite section104 of the workpiece 100 at the right of section 102 has an endelectrode 118, which is also a function electrode of the piezoelectricworkpiece 100. Note that the perspective view of FIG. 1 is toschematically outline the general distribution of the internal electricdipole polarization and is therefore partially shown to be transparent.

[0037] For certain piezoelectric system design requirements, thefunction electrodes of a particular workpiece need to have contours withsharp-turning, or acute, angles. For example, the generally ellipticalshape of the function electrode 110 in the vicinity of the regionidentified by reference numeral 112 in FIG. 1 is considered to besharp-angled. Experiences show that such a sharp angle is likely tocause problem.

[0038] For a typical piezoelectric workpiece such as 100 of FIG. 1, thefunction electrode 110 is frequently paired with another electrode 111adhered to the opposite (bottom) surface of the body of the workpiecehaving a shape contour as illustrated by the phantom-lines. Frequentlywhen this paired electrode 111 is used as the common electrode for theelectric circuit of the piezoelectric system, it typically has arectangular shape.

[0039] In between the pair of electrodes 110 and 111, the crystallinegrains of the body of the workpiece 100 are made to exhibit a grosselectric dipole orientation generally orthogonal to the pair ofelectrodes, as is depicted in the drawing by the vertical arrows betweenthe electrodes 110 and 111.

[0040] Meanwhile, orientation of electric dipoles within the workpiecebody crystalline grains other than those between electrodes 110 and 111is frequently, by design, different. Consider the case in which thepiezoelectric workpiece 100 has another function electrode 118 to thefar right of the body as shown in the drawing. Such a piezoelectricsystem design requires that the grains in the body region generally tothe right of the electrode pair 110 and 111 to exhibit a gross electricdipole orientation different than that in the region between the pair.For example, the gross orientation may need to be substantially parallelto the longitudinal axis of the body of the workpiece, as is illustratedin the drawing by the horizontal arrows.

[0041] Thus, in the case of the workpiece of FIG. 1, there are at leasttwo major electric dipole orientations inside the workpiece bodystructure. In the region generally indicated by reference numeral 114where the two body sections of different electric dipole grossorientations meet, grains of the body material of the workpiece exhibita different physical characteristics that is signified by the abruptalteration of electric dipole moment from one orientation to the other.In the case of the piezoelectric workpiece design of FIG. 1, thisorientation alteration is considered maximum practically at 90 degreessweep from the vertical orientation in the region between the twoelectrodes 110 and 111 to horizontal in the region to the right.

[0042] The boundary region, as generally represented by the region 114,is itself drastically twisted. This is due to, and follows, the sectionof the general contour of the function electrode 110 proximate to theboundary region 114. These declivitous changes in the electric dipoleorientation practically turn the boundary region 114 into a region ofhot spots for accumulation of mechanical stress when the workpiece isoperated to conduct mechanical/electrical energy conversion. Inparticular, stress hot spots arise in areas proximate to thesharp-angled regions of the function electrodes of the piezoelectricworkpiece.

[0043] It is necessary to avoid, at least to smooth, the formation ofregions with abrupt polarization orientation alterations inside the bodyof a piezoelectric workpiece. These regions may lead to mechanicalstress concentrations and eventually result in structural failure,either during the manufacturing phase or normal operation of apiezoelectric workpiece.

[0044] In order to achieve this, in accordance with the presentinvention, augmenting electrically-conductive surface layers that can beused as electrodes during the fabrication phase of piezoelectricworkpieces are implemented. As will be explained in the followingdescription of the present invention, augmenting electrodes for apiezoelectric workpiece for this smoothing purpose are only effectiveduring the fabrication stage of the workpiece. They are functionlessduring the normal operation of the piezoelecteric workpiece.Alternatively, the present invention also proposes to useproperly-shaped and properly-located fabrication-stage augmentingelectrodes instead of permanent surface electrodes for achieving theinventive goal of boundary region smoothing.

[0045]FIG. 2 schematically illustrates the boundary region smoothing ofthe polarization field inside the structural body of a piezoelectricworkpiece 200 of FIG. 1 in accordance with an embodiment of the presentinvention. The smoothing is in the region proximate to the acute-angledarea of the function electrode. The smoothing is achieved via the use ofan augmenting electrode 216 during the fabrication stage while thepoling of the material grains between the two function electrodes 210and 211 is in session.

[0046] Note that in the case of a piezoelectric workpiece such as theone depicted in FIG. 2, the augmenting electrode 216 in a preferredembodiment of the present invention has the shape of agenerally-elongated and, frequently, straightened, or smoothly-curved,band. Such an augmenting band of electrode has its long edgesubstantially aligned with the corresponding edge of therectangular-shaped function electrode 211 located on the oppositesurface of the piezoelectric workpiece.

[0047] For the piezoelectric workpiece of the embodiment of the presentinvention as depicted in FIG.2, poling of the vertical electric dipolesfor the material grains in between the pair of function electrodes 210and 211 is implemented with the participation of the augmentingelectrode 216. Augmenting electrode 216 is electrically connected to thefunction electrode 210 during the poling operation. Together, thefunction electrode 210 and the augmenting electrode 216 constitute agross electrode at the same electric potential that is paired with thecorresponding electrode 211 located on the opposite surface of theworkpiece. With the application of the high poling voltage across thisgross electrode pair, electric dipoles of the grain molecules in theworkpiece generally situated between the pair of gross poling electrodesare gradually turned to their desired (vertical) orientation.

[0048] With the presence of the augmenting electrode 216 during thepoling stage of the fabrication, the drastically-twisted boundary region114 in the case of FIG. 1 can be avoided. Instead, a smoothed region ofboundary generally indicated by reference numeral 214 in FIG. 2 isformed as the poling operation is gradually performed. This smoothing isdue to the presence of the augmenting electrode 216 in the general shapeof an elongated and straightened band. Effectively, this straightenedband 216 assists in smoothing the boundary region between the region ofvertical poling orientation (generally between the function electrodes210 and 211) and its neighboring region to the right (that usually has ahorizontal polarization field).

[0049] Note, again, that the augmenting electrode 216 for thepiezoelectric workpiece 200 of FIG. 2 is only functional during thefabrication phase in particular, the poling processing of the workpiecein the fabrication. As described, the augmenting electrode participatesin turning the electric dipoles so that they align to the desiredorientation with the smoothed boundary region contouring betweensections of a piezoelectric workpiece required to have different bulkpoling orientations. Afterwards, the smoothing augmenting electrode hasno role when the workpiece is operated normally in a piezoelectricsystem.

[0050] Thus, in the case of the piezoelectric workpiece 200 of FIG. 2,while the augmenting electrode 216 can be fabricated as permanentelectrode to reside on the top surface of the body, it can also be atemporary electrode. Such a temporary electrode can be pressedlyattached to the workpiece 200 on its assigned and optimized locationonly during the poling processing stage of the fabrication phase. Afterthe desired poling pattern is established inside the structural body ofthe workpiece, this temporary augmenting electrode can be removed,leaving no trace on the surface of the device at all. A couple ofembodiments of the present invention employing this concept of temporaryaugmenting electrode are shown and described in FIGS. 3-7 as will bedescribed in detail in the following paragraphs.

[0051] In this manner, the boundary region 214 is relatively smoothedwhen compared to the corresponding region 114 in the case of FIG. 1.This is due to the use of the augmenting electrode 216 when theworkpiece is fabricated. The general contour of the augmenting electrode216 proximate to the boundary region 214 is relatively un-curved it isin general in a straight line. This smoothed boundary region 214practically avoids the accumulation of mechanical stress when theworkpiece is operated to conduct mechanical/electrical energyconversion. Reliability of the workpiece is thus improved withoutmechanical stress hot spots.

[0052]FIG. 3 is a top view illustrating the placement of an augmentingsurface layer for a generally elliptically-shaped function electrode inaccordance with the embodiment of the present invention described inFIG. 2. As is shown in the top view, the function electrode 210 isgenerally elliptically shaped, with a sharp-angled end 212 close to theboundary region 214. The augmenting electrode 216 is fabricatedpermanently on the top surface of the workpiece 200 near the boundaryregion 212. The augmenting electrode 216 is fabricated substantially inthe form of an elongated band. Such an augmenting band of electrode,when connected electrically to the function electrode 210 for polingduring the fabrication phase of the workpiece 200, assists in easing andsmoothing the boundary region 214 so that mechanical stress hot spotsare avoided, both during the fabrication phase and normal operation ofthe workpiece.

[0053]FIG. 4 is a top view illustrating the placement of anotheraugmenting surface layer for the generally elliptically-shaped functionelectrode of FIG. 3 in accordance with an embodiment of the presentinvention. As is illustrated, the function electrode 410 is alsogenerally elliptically shaped, with a sharp-angled end 412 close to theboundary region 414. Although the augmenting electrode 416 is fabricatedpermanently on the top surface of the workpiece 400, but unlike in thecase of FIGS. 2 and 3, electrode 416 is made to surround the entirefunction electrode 410. The augmenting electrode 416 is different fromthe augmenting electrode 216 of the workpiece of FIG. 2 in that the itis itself a closed loop that encircles the function electrode entirely.Note, however, that such full enclosure is not a necessary condition toachieve the smoothing of the boundary region as desired.

[0054] The augmenting electrode 416 and the function electrode 410combined as a whole when implementing poling during the fabricationphase, the gross electrode (with electrodes 410 and 416 connectedelectrically to the same voltage) appears substantially equivalent to arectangular electrode. This is despite the presence of the nonconductingband 417 separating the two electrodes. Such an encircling augmentingelectrode 416, when connected electrically to the function electrode 410for the implementation of poling of the workpiece 400, assists toachieve in the easing and smoothing of the boundary region 414.

[0055] Thus, an augmenting electrode can be non-permanent but temporary.These temporary augmenting electrodes being required to be present inthe body system of a workpiece and be functional only during thefabrication phase of the device. FIG. 5 is a top view illustrating thelocation of a fabrication-phase augmenting electrode on the surface of apiezoelectric workpiece in accordance with an embodiment of the presentinvention. This augmenting electrode 516 is non-permanent and has ashape similar to electrode 216 of FIGS. 2 and 3 described above.

[0056] The augmenting electrode 516 can be considered as thenon-permanent, or temporary, type of the corresponding permanentelectrode 416 in the workpiece 400 of FIG. 4. The phantom-lined contourof electrode 516 in the drawing signifies the fact that it is onlypresent during the fabrication phase of the workpiece, and is removedafterwards. FIG. 7 shows such a fabricated workpiece 500, which has onlythe function electrode left on the top surface of the device.

[0057]FIG. 6 is a top view illustrating the location of anotherfabrication-phase augmenting surface electrode on the surface of thepiezoelectric workpiece in accordance with an embodiment of the presentinvention. This augmenting electrode 616 illustrated in phantom-lines isalso non-permanent and has a shape similar to the augmenting electrode416 of FIG. 4 described above. Similarly, the non-permanent augmentingelectrode 616 is the temporary counterpart of electrode 416, and as itsfunctionality is implemented during the fabrication phase of theworkpiece 600, it is not seen on the top surface of the workpiece, as isillustrated in FIG. 7. FIG. 7 is a top view illustrating the electrodepattern of the piezoelectric workpiece of FIGS. 5 and 6 after thecompletion of the fabrication phase thereof.

[0058] Essentially, the two workpieces 500 and 600 of FIGS. 5 and 6,although employing their respective augmenting electrodes 516 and 616during poling operation, are fabricated into workpieces of virtually thesame appearance as shown in FIG. 7. The difference between the two beingthe internal poling characteristics that is not visible from theappearance of the workpieces.

[0059]FIG. 8 schematically illustrates the cross-section of apiezoelectric workpiece without the augmenting surface layer of thepresent invention. The drawing shows the various electrodes of aworkpiece 800 connected to an electric circuit system 830 of thepiezoelectric system 850 for driving a load 840. For example, theelectrode 811, as a common electric node, is connected both to thecircuit loops of the function electrode 810 and that of the functionelectrode 818 of the load 840. In a typical application in which theworkpiece 800 is utilized as a piezoelectric transformer that picks upelectrical energy from the DC power source 830 to drive an AC load 840(such as a cold-cathode fluorescent light, CCFL, tube), the functionelectrode 810 is used as the actuating input electrode and the functionelectrode 818 as the output.

[0060] Without the participation of an augmenting electrode in thefabrication phase, such a prior-art piezoelectric device, as in FIG. 8described above, has an electric dipole poling boundary region 814 thateasily accumulates hot spots of mechanical stress. Such hot spots invitepremature failure of the workpiece, either during the fabrication or thenormal operation of the device.

[0061] In accordance with the teachings of the present invention asdescribed in the previous paragraphs, a piezoelectric workpieceemploying the concept of the inventive augmenting electrodes as outlinedFIG. 9 can be free from such problems. FIG. 9 schematically illustratesa piezoelectric system 950 in which the workpiece is based on that ofFIG. 8 and has incorporated onto itself an augmenting surface layer inaccordance with an embodiment of the present invention. Compared to FIG.8, an additional augmenting electrode 916 is added into the system 950that smoothes the boundary region 914 between the two sections ofdifferent poling characteristics.

[0062] Note, as the drawing shows clearly, the augmenting electrode 916does not take part in the operating mode of the workpiece 900. This isclearly illustrated as the electrode 916 is left unconnectedelectrically in the electrical circuit of the system 950. Also, FIG. 9only shows an application mode of the workpiece 900 as it is connectedin a mechanical/electrical system 950. Note here that the workpiece 900has incorporated a permanent type of augmenting electrode 916 on itssurface.

[0063]FIG. 10 is a cross-sectional view illustrating the contact ofpoling electrodes with both the function and the augmenting surfaceelectrodes in accordance with an embodiment of the present invention.During the poling phase of the fabrication of the workpiece 1000, thefunction electrode 1010 and the augmenting electrode 1016 areelectrically connected together. This common node is then paired withthe node of the electrode 1011, and the pair of nodes is connectedacross the poling voltage V_(Poling). To do this, contact electrodes1061, 1062 and 1063 are used. As is shown in the drawing, contactelectrodes 1061, 1062 and 1063 are pressed with adequate force onto thesurface of their respective function electrodes 1011, 1010 and 1016.

[0064] Since the electrical contact of the contact electrodes with theirrespective workpiece surface electrodes is only necessary during thepoling phase of the device, such contacts are therefore temporary innature. A reasonable scheme to implement these contacts is via the useof adequate fabrication fixture that presses these contact electrodesonto the surface of the workpiece 1000, as is comprehensible to thoseskilled in the art. Also, as is comprehensible, such poling contactsneed to be made under sufficient mechanical pressure to ensure adequateelectrical contact between the poling electrodes and their respectivefunction/augmenting electrodes.

[0065] By contrast, FIG. 11 is a cross-sectional view illustrating thecontact of a poling electrode that is used directly as an augmentingsurface layer in accordance with an embodiment of the present invention.In this described embodiment of the present invention, since there is nopermanent and physical augmenting electrode fabricated onto thecorresponding location on the surface of the workpiece 1100, theaugmenting poling electrode 1116 is directly pressed onto the surface ofthe device.

[0066]FIG. 12 illustrates the point discharge induced at theacute-angled area of a function electrode of a piezoelectric workpiece.As mentioned, such point discharges are likely to occur across theelectrodes used for polarization processing. FIG. 12 depicts a functionelectrode 1210 having a contour with sharp-pointed ends. When a pointdischarge takes place, at the electrode end 1212 near the center of theworkpiece 1200 in particular, the workpiece 1200 is likely to be brokeninto pieces, which is a fatal result. The surge current in associationwith a point discharge across the tipped end 1212 of the functionelectrode 1210 and the corresponding electrode 1211 gives rise to anabrupt increase in local body mechanical stress along the path of thedischarge current. Frequently, such an abrupt regional stress increasebreaks up the workpiece into pieces.

[0067]FIG. 13 illustrates the avoidance of point discharge at theacute-angled area of the function electrode of FIG. 12 in accordancewith an embodiment of the present invention. An augmenting electrode1316 can be placed near the tipped end 1312 of the workpiece 1300 so asto disperse the accumulation of electrical charges, as is illustrated inthe drawing. Note that this augmenting electrode 1316 is also capable ofserving the function of smoothing the polarization boundary region asdescribed above.

[0068] Thus, augmenting electrodes in accordance with the presentinvention are useful for preventing premature failure of a piezoelectricworkpiece while not affecting the functional usefulness of the workpiecein a piezoelectric system. Although the augmenting electrodes describedso far are mainly useful during the fabrication phase of a piezoelectricworkpiece, however, as can be seen in the following paragraphs, anadditional usefulness of the augmenting electrode of the presentinvention can be found during the normal operation of a workpiece.

[0069]FIG. 14 illustrates the piezoelectric workpiece of FIG. 9 havingan additional function electrode. The use of this functional electrode1421 on the body surface of the workpiece 1400 is per design requirementof the piezoelectric system 1450. For example, if the piezoelectricsystem 1450 is engaged in a transformer application as described above,a feedback node 1421 essentially another function electrode isfabricated to the desired location on the surface of the workpiece 1400.As is comprehensible, this feedback node 1421 can be used to pickup upsignal of the workpiece 1400 for feedback to the electric circuit 1430for, for example, implementing a closed loop control scheme in a powertransforming application.

[0070] The use of such a function electrode, which is relativelyisolated spatially, is likely to accumulate electric charges to a leveldangerous to the workpiece itself when the operation of the system isprolonged in time. Sufficient accumulations of electric charges on suchfunction electrodes as 1421 of the system 1450 of FIG. 14 had beenobserved to cause catastrophic results breakage of the piezoelectricworkpiece into pieces.

[0071]FIG. 15 illustrates the piezoelectric workpiece of FIG. 14 havingincorporated another augmenting surface layer in accordance with anembodiment of the present invention. The use of an additional augmentingelectrode 1522 in the system 1550 is advantageous in preventing theseoperational failures. An augmenting electrode 1522 for an isolatedfunction electrode such as 1521 of FIG. 15 is located at a surfacelocation of the workpiece 1500 substantially opposite to the location ofthe electrode 1521. This establishes a symmetry. The symmetry providedby this augmenting electrode 1521 for the spatially isolated functionelectrode 1521 is believed to have concealed the effect of biasedelectric charge accumulation around the spatially isolated electrode1421 as illustrated in FIG. 14. The augmenting electrode 1522 in thecase of FIG. 15 is able to invite the accumulation of its own electriccharges around itself.

[0072] Such induced charge accumulation around augmenting electrode 1522due to that of the function electrode 1521 is believed to have allowedthe evening of the mechanical stress in the vicinity of theseelectrodes. Experimental results had shown the usefulness of theseaugmenting electrodes in preventing breaking of workpieces withspatiallyisolated function electrodes such as for feedback signalpickup. It is necessary to also mention that experimental results hadalso confirmed the usefulness of augmenting electrodes in accordancewith the teachings of the present invention in preventing workpiecebreaking during the poling processing of the fabrication phase.

[0073] For a general rule of implementing an augmenting electrode of thepresent invention for a piezoelectric workpiece in pursuit of improveddevice reliability, FIGS. 16 and 17 provide a couple of examples. FIG.16 illustrates the relative placement of an augmenting surface layer1616 with respect to a relatively irregularly shaped function electrode1610 of a piezoelectric workpiece 1600 in accordance with an embodimentof the present invention. On the other hand, FIG. 17, in accordance withan embodiment of the present invention, illustrates the relativeplacement of another augmenting surface layer 1716 with respect to thefunction electrode 1710 of the piezoelectric workpiece 1700 that isvirtually the same as that of FIG. 16.

[0074] In general, the overall shape of an augmenting electrode at theedge opposite to that facing the function electrode it is intended toaugment is required to have a contour as smooth as possible. This isillustrated in the embodiments as outlined in FIGS. 16 and 17.Specifically, the outer edge of the augmenting electrode 1616 issubstantially circular. In the case of FIG. 17, the outer edge of theaugmenting electrode 1716 is also circular, although its inner edge isas irregular as the contour of its augmented function electrode 1710.

[0075] Thus, a piezoelectric workpiece to be connected in an electriccircuit for energy conversion between electrical and mechanical forms ina piezoelectric system in accordance with a preferred embodiment of thepresent invention would comprise a body, a number of functionelectrodes, and at least an augmenting surface electrode. Note that theaugmenting surface electrode in such embodiment of the invention is apermanent electrode, even though its smoothing functionality is onlyeffective during the fabrication phase of the workpiece.

[0076] The body of piezoelectricity is for implementing the energyconversion. The function electrodes are each fixedly attached to thesurface of the body, and the function electrodes are connected in theelectric circuit for implementing the energy conversion. At least one ofthe function electrodes has a shape with a contour of at least one acuteangle. At least an augmenting surface electrode has a substantiallyelongated shape fixedly attached to the surface of the body proximate tothe acute angle. The augmenting surface electrode and the proximatefunction electrode thereof constitute a gross electrode thatsubstantially cancels the acute angle when both are connectedelectrically to the same electric potential. The acute angle iscancelled during the polarization of electric dipoles of the body grainmolecules so that the boundary region between different polarizationorientation distribution regions can be smoothed. As a result, thereliability of the piezoelectric workpiece is improved both during thefabrication and during normal operation of the workpiece.

[0077] In accordance with an alternate concept of the present invention,the augmenting layer is temporary. Based on such an embodiment, apiezoelectric workpiece comprises a body and a number of functionelectrodes. The body of piezoelectricity is for implementing the energyconversion; and the function electrodes are each fixedly attached to thesurface of the body. The function electrodes are connected in theelectric circuit for implementing the energy conversion. At least one ofthe function electrodes has a shape with a contour of at least one acuteangle, wherein at least a polarization augmenting electrode is pressedonto the surface of the body proximate to the acute angle during thefabrication of the piezoelectric workpiece. The polarization-augmentingelectrode and the proximate function electrode thereof constitute agross electrode when connected electrically together. Similar as in thecase of a permanent augmenting electrode, the gross electrodesubstantially cancels the acute angle when paired with one of thefunction electrodes and connected to a polarization voltage. Thepolarization voltage polarizes electric dipoles of grain molecules ofthe body in between the pair during fabrication of the piezoelectricworkpiece so that the boundary region between different polarizationorientation distribution regions within the piezoelectric workpiece aresmoothed without any acute angle.

[0078] In accordance with the present invention, the method forfabricating a piezoelectric workpiece having permanent augmentingelectrode would comprise at least the following steps. First, a body ofpiezoelectricity for implementing the energy conversion needs to bemade. Then,a number of function electrodes are formed on the surface ofthe body. The function electrodes will be connected in the electriccircuit for implementing the energy conversion. Among the functionelectrodes, at least one has a shape with a contour of at least oneacute angle. At least one polarization augmenting electrode is alsoformed on the surface of the body proximate to the acute angle. Thepolarization-augmenting electrode and the proximate function electrodethereof constitute a gross electrode when connected electricallytogether. Next, electric dipoles of grain molecules of the body arepolarized utilizing the gross electrode, which substantially cancels theacute angle when paired with one of the function electrodes andconnected to a polarization voltage for implementing the polarization.The polarization voltage polarizes electric dipoles of grain moleculesof the body in between the pair so that the boundary region betweendifferent polarization orientation distribution regions within thepiezoelectric workpiece is smoothed without any acute angle.

[0079] An alternative method in accordance with the present inventionthat does not rely on a permanent augmenting electrode to achievesmoothing is also possible. Instead of permanent augmenting electrodes,temporary and equivalent electrodes can be used. The method comprises atleast the following steps. First, a body of piezoelectricity forimplementing the energy conversion is made. Then, a number of functionelectrodes are formed on the surface of the body. Among the functionelectrodes, at least one has a shape with a contour of at least oneacute angle. Then, electric dipoles of grain molecules of the body arepolarized utilizing at least a polarization augmenting electrode pressedonto the surface of the body proximate to the acute angle. Thepolarization augmenting electrode and the proximate function electrodethereof constitutes a gross electrode when connected electricallytogether. Likewise, the gross electrode substantially cancels the acuteangle when paired with one of the function electrodes and connected to apolarization voltage for implementing the polarization. The polarizationvoltage thus may be allowed to polarize electric dipoles of grainmolecules of the body in between the pair so that the boundary regionbetween different polarization orientation distribution regions withinthe piezoelectric workpiece are smoothed without any acute angle.

[0080] Although the invention has been described in considerable detailwith reference to certain preferred versions thereof, other versions arepossible. For example, although the drawings used for the description ofthe preferred embodiment of the present invention include only Rosentype and a couple of other designs, it is not the intention of thepresent invention to be limited to these specific types of piezoelectricworkpieces. Further, although generally-elliptically-shaped functionelectrodes are employed in the drawings, they are not intended for thelimitation to the scope of the present invention. Therefore, the spiritand scope of the appended claims should not be limited to thedescription of the preferred versions contained herein.

1. A method for fabricating a piezoelectric workpiece for an electriccircuit in a piezoelectric system, said method comprising the steps of:a) forming a plurality of function electrodes on the surface of the bodyof said workpiece, said plurality of function electrodes being connectedin said electric circuit of said piezoelectric system; at least one ofsaid function electrodes having a shape with a contour of at least oneacute angle; b) forming at least one polarization augmenting electrodeon the surface of said body proximate to said acute angle, saidpolarization augmenting electrode and said proximate function electrodethereof constituting a gross electrode when connected electricallytogether; and c) polarizing electric dipoles of grain molecules of saidbody utilizing said gross electrode, said gross electrode substantiallycanceling said acute angle when paired with one of said functionelectrodes and connected to a polarization voltage for implementing saidpolarization; and said polarization voltage polarizing electric dipolesof grain molecules of said body in between said pair so that theboundary region between different polarization orientation distributionregions within said piezoelectric workpiece is smoothed without anyacute angle.
 2. The fabricating method of claim 1 wherein said at leastone polarization augmenting electrode has a shape that is substantiallyelongated.
 3. The fabricating method of claim 1 wherein said at leastone polarization augmenting electrode of substantially elongated shapehas at least one smooth edge opposite to said acute angle of saidproximate function electrode.
 4. The fabricating method of claim 1wherein said at least one polarization augmenting electrode has a shapethat is substantially a closed-loop ring surrounding said proximatefunction electrode.
 5. The fabricating method of claim 1 wherein said atleast one polarization augmenting electrode of substantially closed-loopring has at least one smooth edge opposite to said acute angle of saidproximate function electrode.
 6. A method for fabricating apiezoelectric workpiece for electrically connected in an electriccircuit for energy conversion between electrical and mechanical forms ina piezoelectric system, said method comprising the steps of: a) forminga body of piezoelectricity for implementing said energy conversion; andb) forming a plurality of function electrodes on the surface of saidbody, said plurality of function electrodes being connected in saidelectric circuit for implementing said energy conversion; at least oneof said function electrodes having a shape with a contour of at leastone acute angle; c) forming at least one polarization augmentingelectrode on the surface of said body proximate to said acute angle,said polarization augmenting electrode and said proximate functionelectrode thereof constituting a gross electrode when connectedelectrically together; and d) polarizing electric dipoles of grainmolecules of said body utilizing said gross electrode, said grosselectrode substantially canceling said acute angle when paired with oneof said function electrodes and connected to a polarization voltage forimplementing said polarization; and said polarization voltage polarizingelectric dipoles of grain molecules of said body in between said pair sothat the boundary region between different polarization orientationdistribution regions within said piezoelectric workpiece is smoothedwithout any acute angle.
 7. The fabricating method of claim 6 whereinsaid at least one polarization augmenting electrode has a shape that issubstantially elongated.
 8. The fabricating method of claim 7 whereinsaid at least one polarization augmenting electrode of substantiallyelongated shape has at least one smooth edge opposite to said acuteangle of said proximate function electrode.
 9. The fabricating method ofclaim 6 wherein said at least one polarization augmenting electrode hasa shape that is substantially a closed-loop ring surrounding saidproximate function electrode.
 10. The fabricating method of claim 9wherein said at least one polarization augmenting electrode ofsubstantially closed-loop ring has at least one smooth edge opposite tosaid acute angle of said proximate function electrode.
 11. A method forfabricating a piezoelectric workpiece for electrically connected in anelectric circuit for energy conversion between electrical and mechanicalforms in a piezoelectric system, said method comprising the steps of: a)forming a body of piezoelectricity for implementing said energyconversion; and b) forming a plurality of function electrodes on thesurface of said body, said plurality of function electrodes beingconnected in said electric circuit for implementing said energyconversion; at least one of said function electrodes having a shape witha contour of at least one acute angle; and c) polarizing electricdipoles of grain molecules of said body utilizing at least apolarization augmenting electrode pressed onto the surface of said bodyproximate to said acute angle; wherein said polarization augmentingelectrode and said proximate function electrode thereof constituting agross electrode when connected electrically together, said grosselectrode substantially canceling said acute angle when paired with oneof said function electrodes and connected to a polarization voltage forimplementing said polarization; and said polarization voltage polarizingelectric dipoles of grain molecules of said body in between said pair sothat the boundary region between different polarization orientationdistribution regions within said piezoelectric workpiece is smoothedwithout any acute angle.
 12. The fabricating method of claim 11 whereinsaid at least one polarization augmenting electrode has a shape that issubstantially elongated.
 13. The fabricating method of claim 12 whereinsaid at least one polarization augmenting electrode of substantiallyelongated shape has at least one smooth edge opposite to said acuteangle of said proximate function electrode.
 14. The fabricating methodof claim 11 wherein said at least one polarization augmenting electrodehas a shape that is substantially a closed-loop ring surrounding saidproximate function electrode.
 15. The fabricating method of claim 14wherein said at least one polarization augmenting electrode ofsubstantially closed-loop ring has at least one smooth edge opposite tosaid acute angle of said proximate function electrode.
 16. Thefabricating method of claim 11 wherein said at least one polarizationaugmenting electrode is pressed onto the surface of said body onlyduring said fabrication and is removed after said fabrication.